Glenoidal component of a shoulder prosthesis, set of elements constituting such a component and total shoulder prosthesis incorporating such a component

ABSTRACT

The glenoidal component for shoulder prosthesis according to the invention comprises a base adapted to be immobilized on a patient&#39;s glenoid cavity and an element adapted to be added on the base and defining a convex surface of articulation of which at least a part is globally in the form of a portion of sphere and centred on a geometric point, the base being provided with a part centred on an axis and on which is added the afore-mentioned element. When the component is in assembled configuration, the geometric centre and the afore-mentioned axis are offset with respect to each other.

FIELD OF THE INVENTION

The present invention relates to a glenoidal component of a shoulder prosthesis as well as to a set of elements constituting such a component, and to a shoulder prosthesis incorporating such a component.

BACKGROUND OF THE INVENTION

In the domain of shoulder prostheses, it is known for example from U.S. Pat. No. 3,978,528, to constitute a so-called “inverted” prosthesis in which a convex articular surface fast with the glenoid cavity and a concave articular surface fast with the humerus, cooperate in order to recreate a joint at the level of the shoulder. In this type of prosthesis, the glenoidal component may be formed, as disclosed for example in FR-A-2 835 425 or WO-A-01/47442, by a base intended to be immobilized on the glenoid cavity and by an element intended to be mounted on this base and defining the convex surface of articulation.

The invention proposes a novel glenoidal component for a shoulder prosthesis which incorporates a base that may present symmetry of revolution, therefore particularly easy to install, but which also makes it possible to adapt the position of the convex articular surface of the glenoidal component to its environment, particularly to the position of the concave humeral articular surface, while facilitating the work of the deltoid muscle in order to limit as much as possible the efforts to be developed by a patient to raise his/her arm fitted with such a prosthesis.

SUMMARY OF THE INVENTION

In that spirit, the invention relates to a glenoidal component of a shoulder prosthesis comprising a base adapted to be immobilized on the glenoid cavity of a patient, as well as an element adapted to be added on this base and defining the convex surface of articulation of which at least a part is globally in the form of a portion of sphere and centred on a geometric point, this base being provided with a part centred on an axis and on which the afore-mentioned element is added. This component is characterized in that, in assembled configuration, the geometric centre of the spherical portion of the surface of articulation and the axis of the afore-mentioned part of the base are offset with respect to each other.

Thanks to the invention, the position of the centre of symmetry of the spherical portion of the convex articular surface is not necessarily aligned with the central axis of the base, this allowing a satisfactory adjustment of the position of the prosthesis with respect to the scapula.

According to advantageous but non-obligatory aspects, a glenoidal component may incorporate one or more of the following characteristics taken in any technically admissible combination:

The afore-mentioned element defines a housing for at least partially receiving the axisymmetric part of the base, this housing being globally centred on another axis which is offset with respect to the afore-mentioned geometric centre, and, when the component is in assembled configuration, substantially merges with the afore-mentioned axis of the base.

When the component is in implanted configuration on the glenoid cavity, the afore-mentioned geometric centre is offset downwardly of the patient's body with respect to the second axis. This makes it possible in particular to avoid interferences between the humeral component of the prosthesis and the pillar of the scapula at the end of the movement of adduction.

The afore-mentioned element is provided with a rear face into which opens out a housing for at least partially receiving the axisymmetric part of the base, while this housing is centred on an axis merged with the axis of the symmetrical part when the component is in assembled configuration.

The element defines a surface for connection between the part of the articular surface globally in the form of a portion of sphere and a portion of the periphery of this rear face.

The afore-mentioned element is selected from a set of elements adapted to be selectively added on the base and of which the geometric centres have different offsets with respect to the axis of the axisymmetric part of the base. Thanks to this aspect of the invention, the offset may be adjusted as a function of the patient's morphology and of the effective position of anchoring of the base on the glenoid cavity.

The part in the form of a portion of sphere is geometrically centred on an axis parallel to the central axis of the afore-mentioned part of the base.

In a variant, the part in the form of a portion of sphere is geometrically centred on an axis which is not perpendicular to a rear face of the component intended to come into abutment against the patient's glenoid cavity. This aspect of the invention makes it possible to control the orientation of the first axis and to position it correctly, including when the milled surface of the glenoid cavity is not parallel to a vertical plane containing the spinal column of the patient standing up, this occurring particularly when the upper part of the scapula is worn or destroyed.

The invention also relates to a set of elements such as the one mentioned above, which are adapted each to be added, in order to constitute a glenoidal element of a shoulder prosthesis, on a base itself adapted to be immobilized on the glenoid cavity of a patient, each element defining a convex surface of articulation of which at least a part is globally in the form of a portion of sphere centred on a geometric point, while each element forms a globally axisymmetric housing for at least partially receiving a part of the base, and the offset between the afore-mentioned geometric centre and the axis of symmetry of the housing is variable from one element to the other. This set of elements enables the surgeon to select the element with the most appropriate geometry once the base has been immobilized on the patient's glenoid cavity.

The invention also relates to a total shoulder prosthesis which comprises a s glenoidal component as mentioned hereinabove or of which the element which forms the convex surface of articulation has been selected from a set of elements as mentioned hereinabove.

Finally, the invention relates to a method for installing a glenoidal component of a shoulder prosthesis, which may be carried out with a component as described hereinabove and, more specifically, to a method comprising steps consisting in:

immobilizing on the patient's glenoid cavity the base of the glenoidal component;

selecting from a plurality of elements adapted to be added on this base and of which the geometric centres of the parts of articular surfaces in the form of portion of sphere are offset differently with respect to a central axis of a housing for at least partially receiving a part of this base, an element of which the geometric centre of the part of surface in the form of portion of sphere will, once mounted on the base, be in a predetermined position, and

mounting the selected element on the base.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood and other advantages thereof will appear more clearly in the light of the following description of a form of embodiment of a glenoidal component and of a prosthesis in accordance with its principle, given solely by way of example and made with reference to the accompanying drawings, in which:

FIG. 1 schematically shows a shoulder prosthesis according to the invention, implanted on a patient.

FIG. 2 is an exploded view, partially in section, of a glenoidal component of the prosthesis of FIG. 1.

FIG. 3 is a view in perspective of an element constituting the glenoidal component of FIG. 2.

FIG. 4 is a view similar to FIG. 3 for a second element capable of belonging to a glenoidal component as shown in FIG. 2, and

FIG. 5 is a view similar to FIG. 3 for a third element capable of belonging to a glenoidal component as shown in FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings, the prosthesis P shown in FIG. 1 comprises a humeral component 1 composed of a stem 11 intended to be anchored in the medullary canal of the humerus H, as well as of a metaphyseal part 12 in which is immobilized a cup 13 made of polyethylene defining a concave articular surface S₁ in the form of a portion of sphere.

The prosthesis P also comprises a glenoidal component 2 which defines a convex articular surface S₂ and which is intended to be implanted on the glenoid cavity G of the shoulder after the latter has been milled in order to create a surface S_(G) globally parallel to a vertical plane (not shown) containing the spinal column of the patient when he/she is standing up.

In order to render the drawing clearer, the component 1 is shown in section, while the component 2 is shown seen from the outside in FIG. 1.

The surface S₂ comprises a portion S_(2a) globally in the form of a demi-sphere, centred on a geometric point C₂ and of radius R₂.

As is more particularly visible in FIG. 2, the glenoidal component 2 is formed by the assembling of two parts, namely a base 21 and an element 22, sometimes called “head”, which defines the surface S₂ and which is intended to be mounted on the base 21 when the latter has been anchored on the glenoid cavity G.

The base 21 globally presents symmetry of revolution and X₂₁ denotes its central axis. The base 21 comprises a stem 23 for anchoring, intended to be introduced in a corresponding bore to be made in the glenoid cavity G as well as a part 24 intended to project with respect to the surface S_(G) when the base 21 is implanted. The part 24 is truncated and α denotes its semi-vertex angle.

In FIG. 2, the base 21 is shown from the outside, while the head 22 is represented in section in a plane of symmetry.

The head 22 defines a housing 25 for receiving the part 24 when the head 22 is mounted on the base 21. This housing 25 is centred on an axis of symmetry X₂₅ which is merged with the axis X₂₁ when the component 2 is in assembled configuration.

The peripheral surface 25 a of the housing 25 is globally truncated and divergent in the direction of its mouth 25 b, with a semi-vertex angle β of value substantially equal to that of the semi-vertex angle α, this making it possible to obtain an immobilization of the glenoidal head 22 on the base 21 in the manner of a Morse cone.

A bore 26 centred on axis X₂₅ makes it possible to access the housing 25 from the outside, i.e. opposite the surface 27 of the head 22 which is normally turned towards the surface S_(G) milled in the glenoid cavity. This orifice 26 allows the surgeon to manipulate a means for tightening the head 22 on the base 21 such as known, for example, from FR-A-2 835 425.

The centre C₂ of the surface S₂ is not aligned on the axis X₂₅ but offset with respect thereto by a non-zero distance d. X₂ denotes an axis perpendicular to the surface 27 and passing through the centre C₂. This axis is an axis of symmetry of the spherical part S_(2a) of the surface S₂ extended by an imaginary surface of which the trace is represented by the broken arcuate line L_(2a) in FIG. 2. An imaginary hemispherical surface congruent to the part S_(2a) may in effect be considered. The trace of this surface in FIG. 2 would be an arc of circle centred on point C₂ and formed by the join of the arc of circle representing the part S_(2a) and by the line L_(2a). The axis X₂ would in that case be an axis of symmetry of this surface.

The axis X₂ is parallel to axis X₂₅ and, when the head 22 is in mounted configuration, to axis X₂₁.

The centre C₂ defines the position of the part S_(2a) of the surface S₂ which is that which effectively interacts with the surface S₁ of the humeral component 1.

When the glenoidal component 2 is assembled, the centre C₂ is offset with respect to the axis X₂₁ by the distance d which is non-zero, this making it possible to lower the active part S_(2a) of the surface S₂ for a better positioning of the prosthesis with respect to the patient's scapula.

As the portion S_(2a) of the surface S₂ would not allow the head 22 to include the housing 25 taking into account the offset d, an out-of-true transition surface S_(2b) extends the portion S_(2a) up to the edge 27 a of the surface 27 in its part most remote from the centre C₂. The fact that the surface S₂₂ is not hemispherical does not hinder functioning of the prosthesis P insofar as this surface does not normally interact with the surface S₁.

On this subject, it may be imagined, within the scope of the present invention, that the head 22 is truncated in its upper part shown in FIG. 2, i.e. that the surface 25 a is interrupted in its part which projects from the line L_(2a) in FIG. 2, since this part does not normally interact with the surface S₁.

As is more particularly apparent on comparing FIGS. 3 to 5, different heads 22, 22′ and 22″ may be mounted on the base 21, these heads having different offsets d, d′ and d″ between the geometric centres C₂ of the hemispherical portions of the surfaces S₂ that they define and the central axes X₂₅ of the housings 25, 25′, 25″ that they likewise define. The offsets d, d′, d″ correspond, once one of these heads is mounted on a base, to the offsets between the centres C₂ and the axis X₂₁.

In this way, the three glenoidal heads respectively shown in FIGS. 3 to 5 constitute a set of elements that may be selectively added on a base 21 and of which one may be selected by the surgeon after the base has been anchored on the glenoid cavity so that its centre C₂ is in a predetermined position which takes into account the geometry of the glenoid cavity and/or the position of the concave articular surface S₁ of the humeral element.

The installation of a prosthesis according to the invention therefore allows the surgeon, after having anchored the base 21 of the glenoidal component, to adjust the position of the convex articular surface S₂ by a reasoned choice of the glenoidal head 22, 22′, 22″, and this in order to improve the patient's comfort.

When this choice has been effected, it suffices for the surgeon to mount the selected head on the base and to immobilize it by any appropriate means.

According to a variant of the invention (not shown), the axis X₂ of the hemispherical part S_(2a) of the surface S₂ is not necessarily perpendicular to the rear face 28 of the part 24 or to the surface 27 of the head 22 which come into abutment or are parallel to the surface S_(G). This makes it possible to correct a defect in parallelism between the surface S_(G) and the afore-mentioned plane containing the spinal column of the patient in standing position, thanks to a “cant” of the hemispherical part of the surface S₂ with respect to the surface S_(G). 

1. Glenoidal component of a shoulder prosthesis comprising a base adapted to be immobilized on the glenoid cavity of a patient, and an element adapted to be added on said base and defining a convex surface of articulation of which at least a part is globally in the form of a portion of sphere and centred on a geometric point, said base being provided with a part centred on an axis and on which said element is added, wherein, when said component is in assembled configuration, said geometric centre and said axis are offset with respect to each other.
 2. The component of claim 1, wherein said element defines a housing for at least partially receiving said part of said base, said housing being globally centred on an axis which is offset with respect to said geometric centre, and, when the component is in assembled configuration, substantially merges with said axis of said part of said base.
 3. The component of claim 1, wherein the direction of offset between said geometric centre and said axis is such that, when said component is in implanted configuration on the glenoid cavity, said centre is offset downwardly of the patient's body with respect to said axis.
 4. The component of claim 1, wherein said element is provided with a rear face into which opens out a housing for at least partially receiving said part of said base, and said housing is centred on an axis merged with said axis of said part of said base when said component is in assembled configuration.
 5. The component of claim 1, wherein said element defines a surface for connection between the part globally in the form of a portion of sphere of the articular surface and a portion of the periphery of said rear face.
 6. The component of claim 1, wherein said element is selected from a set of elements adapted to be selectively added on said base and of which the geometric centres have different offsets with respect to the axis of said part of said base once mounted thereon.
 7. The component of claim 1, wherein said part in the form of a portion of sphere is geometrically centred on an axis which is parallel to the central axis of said part of said base.
 8. The component of claim 1, wherein said part in the form of a portion of sphere is geometrically centred on an axis non perpendicular to a rear face of said component intended to come into abutment against the patient's glenoid cavity.
 9. Set of elements each adapted to be added, in order to constitute a glenoidal element of a shoulder prosthesis, on a base itself adapted to be immobilized on the glenoid cavity of a patient, each element defining a convex surface of articulation of which at least a part is globally in the form of a portion of sphere centred on a geometric point, while each element forms a globally axisymmetric housing for at least partially receiving a part of said base, and the offset between said geometric centre and the axis of symmetry of the housing is variable from one element to the other.
 10. Total shoulder prosthesis, wherein it comprises the glenoidal component of claim
 1. 11. Total shoulder prosthesis, wherein the element forming the convex surface of articulation belongs to the set of elements of claim
 9. 